The present invention relates to a flow-control valve especially for gasified liquids, for example, for dispensing portions of carbonated water from a storage container for mixing with beverage concentrates in a post-mix beverage-vending machine.
Such a control valve serves to maintain constant, flow quantities per unit of time, in order to achieve high accuracy of the volume of liquid to be dispensed in conjunction with a time limit for dispensing. For example, in beverage-vending machines by means of which refreshment drinks are blended from carbonated water and beverage concentrates, and then presented for consumption, the given blending ratio of the two components must be maintained as precisely as possible, or otherwise variations in taste will occur which affect the quality of the post-mix drink.
A volumetric dosing system is generally employed for the beverage concentrates to be blended in relatively small quantities, thereby again attaining high accuracy in the volumes dispensed.
In order to obtain the requisite accuracy in dispensed volume of the carbonated water and thus to attain the desired blending ratio, the two components determining the volume, namely, the flow quantity and the inlet flow period, must be determined as accurately as possible. The period of flow can be relatively well controlled by means of accurately timed opening and closing valves, although the closing and opening processes can present erroneous values for short dispensing periods.
Control of the flow quantities is considerably more problematic. Briefly occurring variations in pressure and temperature must be considered as well as the fact relative to gasified fluids that the fluid-gas mixture has a tendency to degas in the event of pressure loss, turbulent flow, or heating in the area of the flow-control valve.
In beverage-vending machines the carbonated water is blended in a so-called carbonator from water and CO.sub.2 gas, then stored under pressure and cooled preferably to near the freezing point. Considerable pressure variations arise during the dispensing of carbonated water. Dispensing is carried out in regions of less than atmospheric and hence steady pressure. During long rest periods the flow-control valve is warmed; through the dispensing of carbonated water it is cooled to less than 0.degree. C. High performance standards, however, are expected from such a control valve. Moreover, as an object for commercial production, it should also be inexpensive.
An assembly for mixing liquids using a pressure-independent flow-control valve is already known from German Patent DE 34 30 953. The flow-control valve includes a cylindrical chamber containing a moveable piston driven by the release energy of a spring.
The flowing medium streams through a central hole in the piston to an outlet in the cylinder which is partially covered by the control edge of the piston. The spring counters the force of the medium and applied working pressure. A gap is provided between piston and cylinder with a sealing function. The gap, therefore, is narrow with tight tolerances. Accumulations of dirt between piston and cylinder disturb the control function and lead to erroneous outputs or to breakdown of the assembly. In addition, the relatively complex construction of the conventional control valve with a number of other moveable parts involves the risk of breakdown of the entire assembly if the operational capability of even one single part is adversely affected.